The most common issues when uploading the  routes.yaml file are syntax errors. Ensure that your file complies with the following.

Trailing slashes

If a trailing slash is missed on a URL you'll get an error when uploading the routes.yaml file in the admin.

Example: /about/: is valid but /about: is not

Strict indentation

YAML files use whitespace indentation to denote structure  and using tabs is invalid. Having mismatched indentation is the most common reason for a YAML file not being valid, so ensure to double check your file before you upload to Ghost admin.

Modified the routes.yaml file directly on the server?

If you’ve modified your file directly then Ghost refuses to start if it contains any syntax errors such as missing trailing slashes or indentation issues as mentioned above.